1. Field of the Invention
The present invention generally relates to the conversion of chemical energy to electrical energy. More particularly, the present invention relates to modifying the effective electrochemical surface area of a cell using a mechanically perforated, ion-impermeable fabric disposed between the anode and the cathode. A preferred perforated fabric for a cell having a fluorinated carbon electrode is a Fluorpeel fabric, which is a woven fiberglass cloth impregnated with synthetic resinous fluorine-containing polymers. This material is able to perform its attenuating function while maintaining structural integrity in fluorinated carbon electrode chemistries, which are known to experience swelling during discharge. 2. Prior Art
It is known to use a mechanically perforated film disposed between the anode and the cathode to control the volume of electrolyte passing between the electrodes. U.S. Pat. No. 4,743,520 to Rosansky describes a self-limiting cell including a non-porous, non-electrolyte permeable separator barrier having a predetermined number of openings to dictate the cell's specific design parameters. The prior art separator barrier is made of polyethylene or polypropylene materials and is described as being useful in a wide variety of cell chemistries including lithium-oxyhalide cells having a carbonaceous cathode current collector.
The problem with using polyolefines as separators, and particularly as film separators, is that polyolefinic films possess relatively low mechanical strength and are prone to tearing and puncture, especially during cell swelling. This can defeat the intended purpose of providing the cell with a self-limiting structure in the first place. A perforated separator that ruptures during cell discharge can, at the very least, cause an inaccuracy in the cell's intended discharge performance and, at the worst, cause an internal short circuit condition that may render the cell inoperative and possibly create an explosive venting condition.
Therefore, there exists a need for an electrochemical cell having a discharge modifying structure that is capable of withstanding mechanical stresses such as those caused by electrode swelling, elevated temperatures and shock and vibration forces of the kind experienced in well drilling operations, and the like without the modifying structure rupturing or otherwise becoming structurally compromised.